Police say three of the victims are understood to be British nationals and one is a Vietnamese national.

The Air Accident Investigation Branch is continuing its work to establish the circumstances surrounding the crash between the helicopter and the light aircraft while police and the military began work yesterday (Sunday) on removing the aircraft from the woodland in Upper Winchendon.

The post-mortem examination process in relation to the victims began on Sunday and is expected to last several days.

Police say they will not release the identities of the deceased until after formal identification has taken place however Helicopter Services, based at Wycombe Air Park, put a message out on their Facebook page over the weekend in which they named one of the victims as Captain Mike Green.

The message read: “We are devastated to confirm that Captain Mike Green was involved in the mid-air collision which occurred yesterday.

“Mike was conducting a flight instructor course and was with a student at the time of the incident.

“Both pilots lost their lives.

“We have received many messages of support and kind words about our friend who, as a senior instructor and examiner, helped and mentored so many pilots throughout the industry during his distinguished career.

“It was an honour to work with you. Captain Green, you will be greatly missed.”

Superintendent Rebecca Mears said: “Our thoughts remain with the families of the men who have tragically lost their lives.

“Specially-trained family liaison officers are continuing to offer their support to the families of the victims affected, three of whom we understand to be British nationals, one of whom is a Vietnamese national.

“Work will today focus on removing the aircraft from the scene which will be done with specialist support.

“I would like to reiterate my thanks to the local community for their understanding while the investigation is ongoing in the area.”